Line 4 is 7.4km long and connects two of Budapest's main stations, Kelenföld in Buda and Keleti in Pest. The line interchanges with Line 2 at Keleti and Line 3 at Kálvin Tér.
Alstom has supplied a fleet of 15 five-car Metropolis trains for Line 4. The 80m-long air-conditioned trains can accommodate 810 passengers including 164 seated.
During the first year of operation the trains will be manned by supervisors located in temporary cabs. At the end of this time, Alstom will remove the wall dividing the cab from the passenger area and the trains will be operated without staff on board.
Alstom is also supplying 25 Metropolis trains to replace the existing fleet on Line 2.